feat: support safe recurrence additions

Parse, persist, expand, and round-trip compatible RDATE values while preserving whole-series TUI behavior and conservative rewrite guards.

Verified: normal, warning-as-error, and ASan/UBSan builds pass all 9 suites; storage failure paths preserve calendar and backup bytes; live PTY restores terminal state.

docs/ROADMAP.md

@@ -8,7 +8,8 @@
 - Validated add/edit/delete forms with confirmation and failure rollback
 - Guarded atomic `.ics` persistence, advisory locking, and round-trip tests
 - Bounded session undo/redo, exact external-change detection, and backup recovery
-- Windowed recurrence expansion, EXDATE, IANA TZID, and multi-day segment cues
+- Windowed recurrence expansion, compatible RDATE, EXDATE, IANA TZID, and
+  multi-day segment cues
 - Occurrence-aware appointment search with exact result-to-grid navigation
 - Session calendar toggles shared by month rendering, focus, and search
 - Read-only 42-day agenda with bounded recurrence and exact return navigation
@@ -19,7 +20,8 @@
 
 ## 0.1 — complete local calendar
 
-- Advanced recurrence editing, RDATE/overrides, and embedded VTIMEZONE support
+- Advanced recurrence rule editing and detached RECURRENCE-ID overrides
+- Embedded VTIMEZONE support
 - Screen-reader-friendly linear view and full Unicode display-width handling
 
 ## 0.2 — durable cache and provider boundary